Found this one over on the Tagboard forum and thought it would be a good addition here. It's a simple noise gate with minimal parts count that can easily fit in a 1590a. I've laid it out for a board mounted pot. The schematic calls for a 1M pot, but people have built this using one as low as 25k, so experiment there. The original schematic was a little hard to read so I redrew it.
This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.